Heat transfer apparatus with enhanced micro-channel heat transfer tubing

ABSTRACT

Heat exchange apparatus includes elliptical cross section heat exchange tubing provided with a partition dividing the interior of the tubing into at least two parallel flow passages. The flow passages are delimited by inwardly projecting fins formed on the tubing wall and on the partition, the fins extending parallel to each other and having a height less than the anticipated thickness of the velocity boundary layer of heat exchange fluid flowing through the tubing passages. The tubing may be arranged in serpentine or coiled arrangements of the heat exchange apparatus or parallel tubes extending between heat exchanger header tanks. The heat exchange apparatus is particularly adapted for use in HVAC systems.

BACKGROUND OF THE INVENTION

Apparatus requiring heat transfer from one fluid to another is ubiquitous. For example, heating, ventilating and air conditioning (HVAC) equipment using heat transfer fluids is quite widely used and there is an ever-present need to provide more efficient heat transfer and to reduce the requirements for size and weight of heat transfer equipment as well as the volume of heat transfer fluid required to achieve a particular performance classification. Moreover, in residential and commercial HVAC systems, for example, there is a continuing desire to provide for greater heat transfer and a more compact equipment package to reduce the volume of refrigerant fluid used in the system for environmental and economic reasons.

To achieve the above-mentioned desires, heat transfer apparatus using so called micro-channel heat transfer tubing has been developed. The external dimensions of the heat transfer tubing are relatively small, the tubing is relatively thin walled and a dense, continuous tube type apparatus is provided or a large number of closely spaced apart tubes are provided in the heat exchange apparatus to achieve more efficient heat transfer between a working fluid, such as a vaporizable refrigerant, and ambient air, for example.

One improvement in heat transfer tubing has been to provide the tubing with an arcuate, preferably elliptical, cross section which improves the efficiency of a heat exchanger using such tubing by reducing the resistance to flow of fluid over the external surfaces of the tubing. Outdoor heat exchangers, such as air conditioning condenser units or heat pump heat exchanger units, for example, enjoy the benefits of elliptical shaped heat exchanger tubing. Other applications of heat exchanger apparatus using elliptical tubing may also benefit from this improvement.

However, in the pursuit of greater efficiencies and heat transfer capacity for a given size of heat exchanger or heat transfer apparatus, there has been a continuing desire to provide heat transfer tubing which has an even greater capacity for heat transfer while retaining mechanical strength and durability. It is to these ends that the present invention has been developed.

SUMMARY OF THE INVENTION

The present invention provides an improved heat exchange apparatus including multi-ported heat exchanger tubing with improved heat transfer characteristics. The present invention also provides an improved heat exchanger apparatus utilizing, in particular, multi-ported or multi-passageway heat transfer tubing having a substantially arcuate or curved cross section, either circular or elliptical, for example.

In accordance with one aspect of the present invention, a substantially elliptical cross section heat transfer tube, having relatively small dimensions and being of the so-called micro-channel type, is provided with at least two internal longitudinal parallel flow passages which are separated by a partition, preferably extending along and coincident with the minor axis of the elliptical cross section of the tubing. The wall surfaces of the respective parallel flow passages are provided with heat transfer fins extending longitudinally along the flow passages and being disposed substantially over the entire surface of the tubing wall which defines the flow passages. The fins are of a geometry such that the fin height with respect to the nominal wall surface is less than the thickness of the velocity boundary layer of the fluid flowing through the passages so as to minimize fluid pressure losses of fluid flowing through the passages. The fin height is also defined by an equation disclosed herein and in accordance with the invention. Fins also extend along the surfaces of the wall or partition which defines the multiple flow passages within the tubing.

In accordance with another aspect of the present invention, there is provided a heat transfer apparatus comprising a continuous, elliptical cross section, tubing with multiple flow passages and internal finning in accordance with the invention and wherein the heat transfer apparatus comprises such continuous tubing disposed in a selected geometric pattern. Alternatively, a heat transfer apparatus in accordance with the invention is provided with multiple elliptical cross section heat exchanger tubes in accordance with the invention arranged to extend between manifolds or header tanks such that there is substantial parallel fluid flow through parallel side-by-side arranged heat exchanger tubes.

Heat transfer tubing in accordance with the invention enjoys improved heat transfer performance without materially increasing resistance to fluid flow through the tubing. The combination of the multiple parallel passage, elliptical cross section tubing with heat transfer fins extending in the direction of flow within parallel tubing passages provides an economical heat transfer device with an improved heat transfer performance characteristic.

Those skilled in the art will further appreciate the advantages and superior features of the invention together with other important aspects thereof upon reading the detailed description which follows in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an improved heat transfer tube in accordance with the present invention;

FIG. 2 is a transverse section view of a heat transfer tube in accordance with the invention;

FIG. 3 is a detail view showing a preferred geometry of the heat transfer fins which extend within the internal flow passages of the heat transfer tube shown in FIGS. 1 and 2;

FIG. 4 is a side elevation of one preferred embodiment of a heat transfer apparatus utilizing a continuous heat transfer tube in accordance with the invention;

FIG. 5 is an end view taken from the line 5-5 of FIG. 4 showing the arrangement of the heat transfer tubing in the apparatus of FIG. 4;

FIG. 6 is plan view of another preferred embodiment of a heat transfer apparatus in accordance with the invention;

FIG. 7 is side elevation detail view of the heat transfer apparatus shown in FIG. 6;

FIG. 8 is a side elevation of another embodiment of a heat transfer apparatus in accordance with the invention; and

FIG. 9 is a detail section view taken from the line 9-9 of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the description which follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale and certain features may be shown exaggerated in scale or in somewhat generalized or schematic form in the interest of clarity and conciseness.

Referring to FIG. 1, there is illustrated a heat exchanger or heat transfer tube in accordance with the present invention and generally designated by the numeral 10. The heat transfer tube 10 is preferably of an arcuate, and more preferably elliptical, cross sectional shape and is provided with plural, elongated, parallel, internal flow passages 12 and 14 which are formed in part by a centrally disposed divider or partition 16. The tube 10 also, preferably, includes a continuous outer wall 18 integrally formed with the partition 16, the wall 18 being of substantially constant cross section thickness and the partition 16 being of essentially the same or greater cross section thickness as the wall 18. The tube wall 18 has an outer surface 20 which is essentially uninterrupted but may be provided with heat transfer finning of various types and is shown, by way of example, to have a preferred form of heat transfer finning applied thereto as will be described further herein.

The inner wall surface 21 of the wall 18, as well as the opposed surfaces of the partition 16, is provided with longitudinally extending, closely spaced heat transfer fins, generally designated by the numeral 22 in FIGS. 1 and 2. The tube 10 may be of the so-called micro-channel type wherein the nominal external and internal dimensions of the tube are relatively small, an example of which will be described further herein. Moreover, the fins 22 are preferably integrally formed with the wall 16 and 18 and may also be of a predetermined preferred geometry to be described further herein. The tube 10 may be formed by extrusion processes and may be formed of suitable metals, such as aluminum, or other metals having suitable engineering characteristics with respect to extrusion processes, heat transfer, corrosion resistance and, possibly, the need to be compatible with additional fabrication processes and components contiguous with the tube.

A preferred form of external heat transfer finning is shown for the tube 10 in FIG. 1 as comprising so-called spine finning wherein a strip of heat conductive, continuous, flexible spine fin 24 is applied to the exterior surface 20 of the tube 10 in a known manner and as described further in U.S. Pat. No. 4,535,838 to Gray et al. and U.S. Pat. No. 5,967,228 to Bergman et al., both assigned to the assignee of the present invention. U.S. Pat. Nos. 4,535,838 and 5,967,228 are incorporated herein by reference. Multiple integral spines 26 extend from a side edge strip 28 of the spine finning 24, substantially perpendicular to the outer surface 20 of the tube 10. The spine finning 24 may be secured to the tube 10 in a known manner and as described in the above-referenced patents. The spine finning 24 is preferably helically wrapped tightly around the surface of the tube 10 and in this regard, the elliptical cross section of the tube 10 is suitable for wrapping the spine finning 24 thereon.

Referring now to FIG. 2, a preferred cross sectional geometry of the tube 10 is illustrated. The partition 16 is preferably disposed along and centered on the minor axis 17 of a preferred elliptical cross section geometry of the tube 10. The major axis 19 is, of course, normal to the minor axis 17.

As further shown in FIG. 2, a preferred geometry of the cross section of the tube 10 is such that the width of the tube “a” comprising the extent of the major axis of the elliptical cross section is about twice the height “b” of the tube which is the extent of the minor axis 17. Ratios of width to height, or length of major axis to length minor axis may be of selected values. However, a ratio of a/b of 2:1 is indicated to be satisfactory. The wall thickness “c” of the wall 18 is preferably about equal to or less than the wall thickness “d” of the partition 16 and may be about 75% to 80% of the wall thickness of the partition. As shown in FIG. 2, the interior surface 21 of the wall 18, and the opposed surfaces of the partition 16 which separate the parallel fluid flow passages 12 and 14, are substantially continuously provided with parallel spaced apart inwardly projecting fins 22. The fins 22 are preferably of a height less than the anticipated velocity boundary layer thickness of the fluid flowing through the passages 12 and 14 so as to minimize fluid pressure losses while optimizing heat transfer capacity of tube 10. The height of the fins 22 is preferably determined by the equation: e=2·R ⁷ ·A/P   (1)

wherein e=the fin height, A=cross sectional area of passage 12 or 14, respectively (excluding the fins), P is the cross sectional perimeter length of the passage 12 or 14, respectively, (including the fins) and R is a variable having a value of from 0.6 to 0.95. The value of R is preferably about 0.87.

Referring also to FIG. 3, the detail illustration of the fins 22 indicates that the fins preferably have a trapezoidal shape leaving passage portions 13 between adjacent fins, also having a trapezoidal shape. FIG. 3 indicates that fins 22 of height “e”, have a thickness or width at their peaks “f”, a width “g” at their base, and a spacing “h” between adjacent side edges as illustrated in FIG. 3. For a heat transfer apparatus for use with conventional refrigerant fluids used in commercial and residential HVAC systems, micro-channel tubing, such as the tube 10, may have the following dimensions: a=10.0 mm, b=5.0 mm, c=0.47 mm, d=0.60 mm, e=0.33 mm, f=0.05 mm, g=0.23 mm, and h=0.284 mm. Specific geometries and dimensions given above are for one preferred embodiment of the invention. Those skilled in the art will recognize that these dimensions may be varied somewhat, but for typical heat exchanger tubing of the micro-channel type in accordance with the invention, the dimensions given herein are preferred and advantageous, including the determination of fin height “e” from equation (1).

The enhanced heat exchange tube 10 may be provided in heat transfer apparatus having various configurations. For example, referring to FIG. 4, there is illustrated a heat exchanger 30 characterized by a serpentine arrangement of the tube 10 wherein parallel runs of the tube 10 are indicated at 32. The heat exchanger 30 is formed by bending the tube 10, with or without spine finning 24 applied thereto, to have reverse bends 34. Heat exchanger 30 is typically arranged such that a heat transfer fluid flows through the heat exchanger 30 and over the exterior of tube 10 in the direction of arrow 36, see FIG. 5. The direction of flow of heat exchange fluid, such as ambient air, indicated by arrow 36, is normal to the minor axis 17 of the tube 10 and meets a reduced resistance to fluid flow across the heat exchanger 30. One advantage of the finned partition 16 is that the tube 10 may be bent about radii having respective axes 37, see FIG. 5, parallel to axis 19, without a tendency to collapse the tube and thus reduce the cross sectional area of flow passages 12 and 14.

FIGS. 6 and 7 illustrate another embodiment of a heat exchanger or heat transfer apparatus, generally designated by the numeral 40, having a continuous tube 10 wound in a spiral fashion and arranged such that heat exchange fluid flows through the heat exchanger in the direction of the arrows 36 in FIG. 7. Continuous convolutions 42 are formed in a spiral manner as illustrated in FIG. 7, in particular. The tube 10 may be bent about an axis 37 a parallel to axis 17 so as to present a reduced tube cross section to airflow in the direction of arrows 36 in FIG. 7. Alternatively, the tube 10 may be bent about an axis parallel to axis 19 to form the spiral convolutions. The general configurations of the heat exchangers 30 and 40 are also described, together with the advantages thereof, in U.S. Pat. No. 5,967,228.

Referring to FIGS. 8 and 9, the tube 10, with or without finning 24, (the tube is shown without), may be provided in a heat exchanger 50. Heat exchanger 50 includes opposed manifolds or header tanks 52 and 54 together with a heat exchange fluid inlet 53 and an outlet 55. Heat exchange tubes 10 are arranged as illustrated in FIG. 9 extending between and joined to header tanks 52 and 54. Airflow through the heat exchanger 50 is preferably in the direction of arrow 36 or, of course, in the opposite direction and, normal to the minor axis of the heat exchange tubes 10.

Those skilled in the art will appreciate the advantages and superior features of the invention from the foregoing description. Construction and applications of the heat exchange tube 10, as well as the heat exchangers 30, 40 and 50, may be carried out using conventional engineering practices and materials used for heat exchanger apparatus. Although preferred embodiments of the invention have been described in detail herein, those skilled in the art will also recognize that various substitutions and modifications may be provided without departing from the scope and spirit of the appended claims. 

1. Apparatus for transferring heat between fluids comprising: micro-channel tubing having a generally curved cross sectional shape to be presented to a heat transfer fluid flowing thereover, said cross sectional shape being defined by a wall of said tubing; said tubing including partition means dividing an interior space of said tubing into parallel longitudinal flow passages; and generally parallel, longitudinal, spaced apart fins extending from said wall and said partition means into said flow passages, respectively, to provide enhanced heat transfer between fluids flowing over the exterior of said tubing and within said flow passages, respectively.
 2. The apparatus set forth in claim 1 wherein: said partition means comprises a partition extending along and substantially parallel to an axis of said cross sectional shape of said tubing.
 3. The apparatus set forth in claim 2 wherein: said axis is a minor axis of an ellipse.
 4. The apparatus set forth in claim 3 wherein: said ellipse defines said cross sectional shape of said tubing and said ellipse has a major axis which is approximately twice the length of said minor axis.
 5. The apparatus set forth in said claim 4 wherein: said apparatus is arranged to provide for flow of a heat exchange fluid over the exterior of said tubing generally normal to a minor axis of said elliptical cross section.
 6. The apparatus set forth in claim 1 wherein: the cross sectional shape of said tubing is substantially elliptical.
 7. The apparatus set forth in claim 6 wherein: said apparatus is formed as a serpentine coil of said tubing and said tubing is bent in reverse bends about an axis substantially parallel to a major axis of said elliptical cross sectional shape.
 8. The apparatus set forth in claim 6 wherein: said apparatus is formed in a continuous helical coil of said tubing which is bent about an axis substantially parallel to a major axis of said elliptical cross sectional shape.
 9. The apparatus set forth in claim 1 wherein: said fins have a substantially trapezoidal cross sectional shape.
 10. The apparatus set forth in claim 1 wherein: the height of said fins is less than the thickness of a velocity boundary layer of fluid flowing through said flow passages, respectively.
 11. The apparatus set forth in claim 10 wherein: the height of said fins is determined from the equation e=2·R⁷·A/P where e=height of said fins, R is a variable having a value of from about 0.60 to 0.95, A is the cross sectional area of one of said flow passages and P is the perimeter length of said one flow passage.
 12. The apparatus set forth in claim 1 wherein: the thickness of said wall is in a range of about 70% to 80% of the thickness of said partition means.
 13. Apparatus for transferring heat between fluids comprising: micro-channel tubing having a generally elliptical cross sectional shape to be presented to a heat transfer fluid flowing thereover, said cross sectional shape being defined by a wall of said tubing; said tubing including a partition extending along and substantially parallel to an axis of said cross sectional shape of said tubing and dividing an interior space of said tubing into parallel longitudinal flow passages; and generally parallel, longitudinal, spaced apart fins extending from said wall and said partition into said flow passages, respectively, said fins having a height less than the thickness of a velocity boundary layer of a fluid flowing through said flow passages to provide enhanced heat transfer between fluids flowing over the exterior of said tubing and within said flow passages, respectively.
 14. The apparatus set forth in claim 13 wherein: said axis is a minor axis of said elliptical cross sectional shape of said tubing.
 15. The apparatus set forth in claim 14 wherein: said elliptical cross sectional shape of said tubing has a major axis which is approximately twice the length of said minor axis.
 16. The apparatus set forth in claim 13 wherein: said fins have a substantially trapezoidal cross sectional shape.
 17. The apparatus set forth in claim 13 wherein: said apparatus is formed as a serpentine coil of said tubing and said tubing is bent in reverse bends about an axis substantially parallel to a major axis of said elliptical cross sectional shape.
 18. The apparatus set forth in claim 13 wherein: said apparatus is formed in a continuous helical coil of said tubing which is bent about an axis substantially parallel to a major axis of said elliptical cross sectional shape.
 19. Micro-channel tubing for transferring heat between fluids and having a generally curved cross sectional shape to be presented to a heat transfer fluid flowing thereover, said cross sectional shape being defined by a wall of said tubing; said tubing including at least one partition dividing an interior space of said tubing into parallel longitudinal flow passages; and generally parallel, longitudinal, spaced apart fins extending from said wall and said partition, respectively, into said flow passages, respectively, to provide enhanced heat transfer between fluids flowing over the exterior of said tubing and within said flow passages, respectively, said fins having a substantially trapezoidal cross sectional shape and a height less than the thickness of a velocity boundary layer of fluid flowing through said flow passages.
 20. The tubing set forth in claim 19 wherein: said cross sectional shape of said tubing is elliptical and includes a major axis and a minor axis and said partition is coincident with said minor axis.
 21. The tubing set forth in claim 20 wherein: the length of said major axis is about twice the length of said minor axis.
 22. The tubing set forth in claim 19 wherein: the height of said fins is determined from the equation e=2·R⁷·A/P where e=height of said fins, R is a variable having a value of from about 0.60 to 0.95, A is the cross sectional area of one of said flow passages and P is the perimeter length of said one flow passage.
 23. Micro-channel tubing for transferring heat between fluids and having a generally curved cross sectional shape to be presented to a heat transfer fluid flowing thereover, said cross sectional shape being defined by a wall of said tubing; said tubing including at least one partition dividing an interior space of said tubing into parallel longitudinal flow passages; and generally parallel, longitudinal, spaced apart fins extending from said wall and said partition, respectively, into said flow passages, respectively, to provide enhanced heat transfer between fluids flowing over the exterior of said tubing and within said flow passages, respectively, said fins having a height determined from the equation e=2·R⁷·A/P where e=height of said fins, R is a variable having a value of from about 0.60 to 0.95, A is the cross sectional area of one of said flow passages and P is the perimeter length of said one flow passage.
 24. The tubing set forth in claim 23 wherein: R has a value of about 0.87. 